Many ink-jet printers employ as a supply of ink a cartridge which serves as a reservoir of ink and which also provides direct fluid communication to a printhead assembly on the cartridge for jetting droplets of ink toward a print medium, such as paper. It is important to provide a constant negative pressure to the ink to resist the flow of ink through the nozzles in the printhead.
Plotters employing the ink-jet principle often require a supply of ink that exceed that available in cartridge form. An example of means for storing a supply of ink is disclosed and claimed in U.S. Pat. No. 4,714,937, issued to George Kaplinsky and assigned to the same assignee as this application. Briefly, a reservoir of ink is used to refill a bladder, which collapses as the ink is consumed. The collapsing bladder, which comprises an elastomeric material, exerts the desired negative, or back, pressure during collapse to prevent the ink contents from draining out except upon demand. When the bladder is substantially emptied, it is refilled from the reservoir.
In cartridges used in printers and in bladders used in plotters, it has been determined that the material used to fabricate the cartridge or bladder is crucial to the operation of the pen. Specifically, many elastomer formulations used in such cartridges and bladders are found to contain soluble or partially soluble components that dissolve in aqueous-based inks. Such soluble or partially soluble components contaminate the ink and may affect ink properties and cause aberrant printing behavior. Properties that may change include surface tension, viscosity, and pH. Further, as ink extracts materials from the bladder, or otherwise attacks the elastomer, the bladder characteristics will change, resulting in a back-pressure variation that may be unacceptable. Finally, water loss through the bladder membrane is an important consideration. If the water content of the ink drops, then the ink will deliver non-optimal performance in several areas, including color, crusting time, viscosity, and surface tension.
Thus, there is a need to provide an elastomeric material which does not contaminate aqueous-based inks used in ink-jet printing and which minimizes loss of water from the ink.